This is a note to let you know that I've just added the patch titled
napi: fix race inside napi_enable
to the 5.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
napi-fix-race-inside-napi_enable.patch
and it can be found in the queue-5.14 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit e66cad414e6f11dd5921096760711ca2a37ed8c3
Author: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
Date: Sat Sep 18 16:52:32 2021 +0800
napi: fix race inside napi_enable
[ Upstream commit 3765996e4f0b8a755cab215a08df744490c76052 ]
The process will cause napi.state to contain NAPI_STATE_SCHED and
not in the poll_list, which will cause napi_disable() to get stuck.
The prefix "NAPI_STATE_" is removed in the figure below, and
NAPI_STATE_HASHED is ignored in napi.state.
CPU0 | CPU1 | napi.state
===============================================================================
napi_disable() | | SCHED | NPSVC
napi_enable() | |
{ | |
smp_mb__before_atomic(); | |
clear_bit(SCHED, &n->state); | | NPSVC
| napi_schedule_prep() | SCHED | NPSVC
| napi_poll() |
| napi_complete_done() |
| { |
| if (n->state & (NPSVC | | (1)
| _BUSY_POLL))) |
| return false; |
| ................ |
| } | SCHED | NPSVC
| |
clear_bit(NPSVC, &n->state); | | SCHED
} | |
| |
napi_schedule_prep() | | SCHED | MISSED (2)
(1) Here return direct. Because of NAPI_STATE_NPSVC exists.
(2) NAPI_STATE_SCHED exists. So not add napi.poll_list to sd->poll_list
Since NAPI_STATE_SCHED already exists and napi is not in the
sd->poll_list queue, NAPI_STATE_SCHED cannot be cleared and will always
exist.
1. This will cause this queue to no longer receive packets.
2. If you encounter napi_disable under the protection of rtnl_lock, it
will cause the entire rtnl_lock to be locked, affecting the overall
system.
This patch uses cmpxchg to implement napi_enable(), which ensures that
there will be no race due to the separation of clear two bits.
Fixes: 2d8bff12699abc ("netpoll: Close race condition between poll_one_napi and napi_disable")
Signed-off-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
Reviewed-by: Dust Li <dust.li@xxxxxxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/net/core/dev.c b/net/core/dev.c
index 8f1a47ad6781..693f15a05630 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -6988,12 +6988,16 @@ EXPORT_SYMBOL(napi_disable);
*/
void napi_enable(struct napi_struct *n)
{
- BUG_ON(!test_bit(NAPI_STATE_SCHED, &n->state));
- smp_mb__before_atomic();
- clear_bit(NAPI_STATE_SCHED, &n->state);
- clear_bit(NAPI_STATE_NPSVC, &n->state);
- if (n->dev->threaded && n->thread)
- set_bit(NAPI_STATE_THREADED, &n->state);
+ unsigned long val, new;
+
+ do {
+ val = READ_ONCE(n->state);
+ BUG_ON(!test_bit(NAPI_STATE_SCHED, &val));
+
+ new = val & ~(NAPIF_STATE_SCHED | NAPIF_STATE_NPSVC);
+ if (n->dev->threaded && n->thread)
+ new |= NAPIF_STATE_THREADED;
+ } while (cmpxchg(&n->state, val, new) != val);
}
EXPORT_SYMBOL(napi_enable);
